Patients who have been implanted with a medical device including a pulse generator and a lead system, such as a cardiac pacemaker or a defibrillator, are sometimes subjected to electromagnetic energy. A magnetic resonance imaging (MRI) procedure is one example of a procedure where a patient is subjected to electromagnetic energy. An MRI uses a powerful magnetic field, radiofrequency (RF) waves, and a rapidly changing magnetic field to demonstrate whether or not there is an injury or some disease process present. MRI is an efficient technique used in the diagnosis of many disorders, including neurological and cardiac abnormalities and other diseases. MRI has achieved prominence in both the research and clinical arenas. It provides a non-invasive method for examining internal body structures and functions. Because MRI has become such a useful diagnostic tool, it now is used extensively in hospitals and clinics around the world.
One problem associated with MRI scanning of a patient having a pulse generator and lead system is that the RF excitation output from the MRI scanner can be coupled into a lead conductor and then delivered as current out of the lead at the interface between a lead electrode and body tissue. The current density at the lead electrode can be sufficient to cause appreciable current loss in the body tissue, resulting in heat generation. This RF-induced heating may cause tissue damage at the electrode/tissue interface, as well as negatively affect performance of the medical device.
One method of reducing RF-induced heating at an electrode/tissue interface is the inclusion of an RF choke component near the electrode, generally at a distal end of the lead. Such RF choke components are typically insulated coils having inductive and capacitive effects that reduce the flow of current. The RF choke component thus acts as an electromagnetic filter and/or trap that blocks RF excitation currents from flowing through the electrode. Another method of reducing RF-induced heating at an electrode/tissue interface is shielding the lead conductor from RF energy.
Current devices and methods for reducing RF-induced heating in pulse generator and lead systems require additional lead components or materials, and therefore increase the cost and bulk of the lead system. Thus, there is a need in the art for an RF choke assembly that minimizes the number of additional components and materials. There is a further need in the art for an RF choke assembly that does not significantly increase the cost and bulk of the lead system.